Wednesday, June 16, 2004

A flaw in the Linux kernel allows a 20-line C program to crash most distributions using the 2.4 and 2.6 kernels running on x86 and x86-64 architectures, according to security researchers.
The problem means that anyone with an ordinary user account on a Linux machine can crash the entire server, according to Oyvind Saether, who discovered the bug along with Stian Skjelstad. Administrator access isn't required.

"Using this exploit to crash Linux systems requires the (ab)user to have shell access or other means of uploading and running the program (like cgi-bin and FTP access)," Saether wrote in an advisory on Friday. "This exploit has been reportedly used to take down several lame free-shell providers' servers."

Linux developers released a kernel patch to coincide with the advisory, available on Kernel.org. Major Linux vendors have also begun releasing their own versions of the fix, including Red Hat Inc.'s Fedora Project and Gentoo Linux.

The most recent updates to the Linux kernel, to be available in Version 2.6.7, fix the problem, according to Linus Torvalds. The new version is expected to be available today.

The bug is in the way the kernel handles floating point exceptions, developers said. While it is serious, two factors limit the danger: It can be exploited only by someone with a valid user account, and it doesn't allow the attacker to gain control of the system.